1. Field of the Invention
The present invention relates to an optical information recording medium permitting the recording and reproducing of information with a laser beam, and more particularly, to a heat mode optical information recording medium suited to the recording and reproducing of information with a short-wavelength laser beam with a wavelength of equal to or shorter than 440 nm and to a method of recording information on the optical information recording medium by irradiation of a short-wavelength laser beam with a wavelength of equal to or shorter than 440 nm.
The present invention further relates to a novel azo metal complex dye suitable for use as a dye in the recording layer of an optical information recording medium.
2. Discussion of the Background
The recordable CD (CD-R) and recordable DVD (DVD-R) have been known as optical information recording media permitting the “write-once” recording of information with a laser beam. In contrast to the recording of information on a CD-R, which is conducted with a laser beam in the infrared range (normally, at a wavelength of about 780 nm), the recording of information on a DVD-R is conducted with a visible light laser beam (with a wavelength of about 630 to 680 nm). Since a recording laser beam of shorter wavelength is employed for a DVD-R than for a CD-R, the DVD-R has an advantage of being able to record at higher density than on a CD-R. Thus, the status of the DVD-R as a high-capacity recording medium has to some degree been ensured in recent years.
Networks, such as the Internet, and high-definition television have recently achieved widespread popularity. With high-definition television (HDTV) broadcasts near at hand, demand is growing for high-capacity recording media for recording image information both economically and conveniently. However, the CD-R and DVD-R do not afford recording capacities that are adequate to handle future needs. Accordingly, to increase the recording density by using a laser beam of even shorter wavelength than that employed in a DVD-R, the development of high-capacity disks capable of recording with laser beams of short wavelength is progressing. For example, an optical recording disk known as the “Blu-ray,” employing a blue laser of 405 nm, and HD-DVD have been proposed.
For example, Reference 1 (Japanese Unexamined Patent Publication (KOKAI) Heisei No. 11-310728), Reference 2 (Japanese Unexamined Patent Publication (KOKAI) Heisei No. 11-130970), Reference 3 (Japanese Unexamined Patent Publication (KOKAI) No. 2002-274040), and Reference 4 (Japanese Unexamined Patent Publication (KOKAI) No. 2000-168237), which are expressly incorporated herein by reference in their entirety, propose the use of azo metal complex dyes as dyes contained in the recording layer in DVD-R optical disks. These azo metal complex dyes have absorption waveforms corresponding to red lasers, and cannot achieve adequate recording characteristics in recording by laser beams of short wavelength (for example, 405 nm).
Accordingly, in optical recording disks employing short-wavelength laser beams (such as a 405 nm blue laser beam), attempts are being made to shorten the absorption wavelength of the azo metal complexes employed in DVD-Rs. These attempts are disclosed in, for example, Reference 5 (Japanese Unexamined Patent Publication (KOKAI) No. 2001-158862), Reference 6 (Japanese Unexamined Patent Publication (KOKAI) No. 2006-142789), Reference 7 (Japanese Unexamined Patent Publication (KOKAI) No. 2006-306070) or English language family member EP 1 864 822 A1, which are expressly incorporated herein by reference in their entirety.
We evaluated the light resistance of the dye films and the recording and reproduction characteristics of optical information recording media corresponding to short wavelength lasers, such as blue lasers, for the azo metal complexes described in References 5 to 7. As a result, we found that none of these azo metal complexes achieved both light resistance and recording and reproduction characteristics (jitter and reproduction durability).